diff --git a/pymc/distributions/transforms.py b/pymc/distributions/transforms.py
index ebdaf3c3e..4e59049d3 100644
--- a/pymc/distributions/transforms.py
+++ b/pymc/distributions/transforms.py
@@ -300,7 +300,7 @@ def __init__(self, zerosum_axes):
 
     @staticmethod
     def extend_axis(array, axis):
-        n = (array.shape[axis] + 1).astype("floatX")
+        n = pt.cast(array.shape[axis] + 1, "floatX")
         sum_vals = array.sum(axis, keepdims=True)
         norm = sum_vals / (pt.sqrt(n) + n)
         fill_val = norm - sum_vals / pt.sqrt(n)
@@ -312,7 +312,7 @@ def extend_axis(array, axis):
     def extend_axis_rev(array, axis):
         normalized_axis = normalize_axis_tuple(axis, array.ndim)[0]
 
-        n = array.shape[normalized_axis].astype("floatX")
+        n = pt.cast(array.shape[normalized_axis], "floatX")
         last = pt.take(array, [-1], axis=normalized_axis)
 
         sum_vals = -last * pt.sqrt(n)
diff --git a/tests/distributions/test_transform.py b/tests/distributions/test_transform.py
index e28052bab..176bc24ce 100644
--- a/tests/distributions/test_transform.py
+++ b/tests/distributions/test_transform.py
@@ -170,6 +170,17 @@ def test_sum_to_1():
     )
 
 
+def test_zerosumtransform():
+    zst = tr.ZeroSumTransform([0])
+
+    # Check numpy input works, as it is not always converted to pytensor before
+    # Case where it failed was when setting initvals in model
+    val = np.array([1, 2, 3, 4])
+    zval = zst.backward(val)
+    assert np.allclose(zval.eval().sum(), 0.0)
+    assert np.allclose(zst.forward(zval).eval(), val)
+
+
 def test_log():
     check_transform(tr.log, Rplusbig)